1. Field of the Invention
The present invention relates generally to methods and compositions for the respiratory delivery of insulin to diabetic patients. More particularly, the present invention relates to the pulmonary delivery of dry powder insulin preparations for rapid systemic absorption through the lungs.
Insulin is a 50 amino acid polypeptide hormone having a molecular weight of about 6,000 which is produced in the pancreatic xcex2-cells of normal (non-diabetic) individuals. Insulin is necessary for regulating carbohydrate metabolism by reducing blood glucose levels, and a systemic deficiency causes diabetes. Survival of diabetic patients depends on the frequent and long-term administration of insulin to maintain acceptable blood glucose levels.
Insulin is most commonly administered by subcutaneous injection, typically into the abdomen or upper thighs. In order to maintain acceptable blood glucose levels, it is often necessary to inject insulin at least once or twice per day, with supplemental injections of rapid-acting insulin being administered when necessary. Aggressive treatment of diabetes can require even more frequent injections, where the patient closely monitors blood glucose levels using home diagnostic kits. The present invention is particularly concerned with the administration of rapid acting insulins which are able to provide serum insulin peaks within one hour and glucose troughs within 90 minutes.
The administration of insulin by injection is undesirable in a number of respects. First, many patients find it difficult and burdensome to inject themselves as frequently as necessary to maintain acceptable blood glucose levels. Such reluctance can lead to non-compliance, which in the most serious cases can be life-threatening. Moreover, systemic absorption of insulin from subcutaneous injection is relatively slow, frequently requiring from 45 to 90 minutes, even when fast-acting insulin formulations are employed. Thus, it has long been a goal to provide alternative insulin formulations and routes of administration which avoid the need for self-injection and which can provide rapid systemic availability of the insulin.
A variety of such alternative insulin administration roots have been proposed, including intranasal, intrarectal, and intravaginal.
While these techniques avoid the discomfort and poor compliance associated with subcutaneous injection, they each suffer from their own limitations. Intrarectal and intravaginal are inconvenient, uncomfortable, and the latter is not available to the entire population of diabetics. Intranasal delivery would be convenient and probably less objectionable than injection, but requires the use of potentially toxic xe2x80x9cpenetration enhancersxe2x80x9d to effect passage of insulin across the nasal mucosa, which is characterized by a thick epithelial layer which is resistant to the passage of macromolecules. Of particular interest to the present invention is pulmonary insulin delivery where a patient inhales an insulin formulation and systemic absorption occurs through the thin layer of epithelial cells in the alveolar regions of the lung. Such pulmonary insulin delivery appears to provide more rapid systemic availability than does subcutaneous injection and avoids the use of a needle. Pulmonary insulin delivery, however, has yet to achieve widespread acceptance. Heretofore, pulmonary delivery has been most often accomplished through nebulization of liquid insulin formulations, requiring the use of cumbersome liquid nebulizers. Moreover, the aerosols formed by such nebulizers have a very low insulin concentration, necessitating a large number of inhalations to provide an adequate dosage. Insulin concentration is limited due to the low solubility of insulin in suitable aqueous solutions. In some cases, as many as 80 or more breaths may be required to achieve an adequate dosage, resulting in an administration time from 10 to 20 minutes, or more.
It would be desirable to provide improved methods and compositions for the pulmonary delivery of insulin. It would be particularly desirable if such methods and compositions were sufficiently convenient to permit self-administration even away from home and were able to deliver a desired total dosage with a relatively low number of breaths, preferably fewer than ten. Such methods and compositions should also provide for rapid systemic absorption of the insulin, preferably reaching a serum peak within 45 minutes or less and a resulting glucose trough within about one hour or less. Such rapid acting formulations will preferably be suitable for use in aggressive treatment protocols where injection of intermediate and long-acting insulin can be reduced or eliminated. The compositions of the present invention should also be stable, preferably consisting of a concentrated dry powder formulation.
2. Description of the Background Art
The respiratory delivery of aerosolized aqueous insulin solutions is described in a number of references, beginning with Gxc3xa4nsslen (1925) Klin. Wochenschr. 4:71 and including Laube et al. (1993) JAMA 269:2106-21-9; Elliott et al. (1987) Aust. Paediatr. J. 23:293-297; Wigley et al. (1971) Diabetes 20:552-556. Corthorpe et al. (1992) Pharm Res 9:764-768; Govinda (1959) Indian J. Physiol. Pharmacol. 3:161-167; Hastings et al. (1992) J. Appl. Physiol. 73:1310-1316; Liu et al. (1993) JAMA 269:2106-2109; Nagano et al. (1985) Jikeikai Med. J. 32:503-506; Sakr (1992) Int. J. Phar. 86:1-7; and Yoshida et al. (1987) Clin. Res. 35:160-166. Pulmonary delivery of dry powder medicaments, such as insulin, in a large particle carrier vehicle is described in U.S. Pat. No. 5,254,330. A metered dose inhaler (MDI) for delivering crystalline insulin suspended in a propellant is described in Lee and Sciara (1976) J. Pharm. Sci. 65:567-572. A MDI for delivering insulin into a spacer for regulating inhalation flow rate is described in U.S. Pat. No. 5,320,094. The intrabronchial administration of recombinant insulin is briefly described in Schluter et al. (Abstract) (1984) Diabetes 33:75A and Kxc3x6bhler et al. (1987) Atemw. Lungenkrkh. 13:230-232. Intranasal and respiratory delivery of a variety of polypeptides, including insulin, in the presence of an enhancer, are described in U.S. Pat. No. 5,011,678 and Nagai et al. (1984) J. Contr. Rel. 1:15-22. Intranasal delivery of insulin in the presence of enhancers and/or contained in controlled release formulations are described in U.S. Pat. Nos. 5,204,108; 4,294,829; and 4,153,689; PCT Applications WO 93/02712, WO 91/02545, WO 90/09780, and WO 88/04556; British Patent 1,527,605; Rydxc3xa9n and Edman (1992) Int. J. Pharm. 83:1-10; and Bjxc3x6rk and Edman (1988) Int. J. Pharm. 47:233-238. The preparation and stability of amorphous insulin were described by Rigsbee and Pikal at the American Association of Pharmaceutical Sciences (AAPS), Nov. 14-18, 1993, Lake Buena Vista, Fla. Methods for spray drying polypeptide, polynucleotide and other labile drugs in a carrier which forms an amorphous structure which stabilize the drug are described in European patent application 520 748.
According to the present invention, methods and compositions for the aerosolization and systemic delivery of insulin to a mammalian host, particularly a human patient suffering from diabetes, provide for rapid absorption into blood circulation while avoiding subcutaneous injection. In particular, the methods of the present invention rely on pulmonary delivery of insulin in the form of a dry powder. Surprisingly, it has been found that inhaled dry insulin powders are deposited in the alveolar regions of the lung and rapidly absorbed through the epithelial cells of the alveolar region into blood circulation. Thus, pulmonary delivery of insulin powders can be an effective alternative to administration by subcutaneous injection.
In a first aspect of the present invention, insulin is provided as a dry powder, usually but not necessarily in a substantially amorphous state, and dispersed in an air or other physiologically acceptable gas stream to form an aerosol. The aerosol is captured in a chamber having a mouthpiece, where it is available for a subsequent inhalation by a patient. Optionally, the dry powder insulin is combined with a pharmaceutically acceptable dry powder carrier, as described in more detail below. The insulin powder preferably comprises particles having a diameter less then 10 xcexcm, more preferably less than 7.5 xcexcm, and most preferably below 5 xcexcm, usually being in the range from 0.1 xcexcm to 5 xcexcm. Surprisingly, it has been found that the dry powder insulin compositions of the present invention are absorbed in the lung without the use of penetration enhancers such as those required for absorption through the nasal mucosa and upper respiratory tract.
In a second aspect, the present invention provides insulin compositions consisting essentially of dry powder insulin having an average particle size below 10 xcexcm which may be combined with dry powder pharmaceutical carriers. The insulin composition is preferably free from penetration enhancers and comprises particles having a diameter less than 10 xcexcm, preferably less than 7.5 xcexcm, and most preferably below 5 xcexcm, usually being in the range from 0.1 xcexcm to 5 xcexcm. Usually, the insulin dry powder will have from 5% to 99% by weight insulin in the composition, more usually from 15% to 80%, in a suitable pharmaceutical carrier, usually a carbohydrate, an organic salt, an amino acid, peptide, or protein, as described in more detail hereinafter.
In a third aspect of the present invention, insulin dry powders are prepared by dissolving insulin in an aqueous buffer to form a solution and spray drying the solution to produce substantially amorphous particles having a particle size less than 10 xcexcm, preferably less than 7.5 xcexcm, and most preferably below 5 xcexcm, usually being in the range from 0.1 xcexcm to 5 xcexcm. Optionally, the pharmaceutical carrier is also dissolved in the buffer, to form a homogeneous solution, wherein spray drying of the solution produces individual particles comprising insulin, carrier buffer, and any other components which were present in the solution. Preferably the carrier is a carbohydrate, organic salt, amino acid, peptide, or protein which produces a substantially amorphous structure upon spray drying. The amorphous carrier may be either glassy or rubbery and enhances stability of the insulin during storage. Advantageously, such stabilized formulations are also able to effectively deliver insulin to the blood stream upon inhalation to the alveolar regions of the lungs.
A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.